A typical device for manufacturing an electrolytic copper foil comprises a metal cathode drum and an insoluble metal anode, the metal cathode drum being rotatable and having a mirror polished surface. The insoluble metal anode is arranged at approximately the lower half of the metal cathode drum and surrounds the metal cathode drum. A copper foil is continuously manufactured with the device by flowing a copper electrolytic solution between the cathode drum and the anode, applying direct current between these to allow copper to be electrodeposited on the cathode drum, and detaching an electrodeposited copper foil from the cathode drum when a predetermined thickness is obtained.
The copper foil is often used as a negative current collector for lithium-ion secondary batteries and for printed wiring boards. Lithium-ion secondary batteries include a positive electrode, a negative electrode, and an electrolyte. The negative electrode typically includes carbon particles applied as a negative electrode active material layer to the surface of a negative current collector made from the copper foil. As the negative electrode active substance, carbon-based materials such as graphite capable of absorbing/desorbing lithium ions are commonly used. More recently, silicon-based materials or tin-based materials having a larger theoretical capacity than graphite-based materials have been proposed. Lithium-ion secondary batteries are used in electronic devices such as cell-phones, video cameras, and personal computers. Along with downsizing of the electronic devices, downsizing and capacity increase of the lithium-ion secondary batteries are progressing. Initial charging capacity and charge-discharge property are particularly important among properties required for the lithium-ion secondary batteries.